The invention relates generally to the reduction of electric motor structure-borne noise in engine cooling applications and, more particularly, to an effective way of isolating the motor""s vibration from the rest of the vehicle to reduce in-vehicle structure-borne noise.
In typical engine cooling modules, a DC permanent magnet motor is employed to drive a fan. The magnets of the electric motor are subjected to many fluctuating forces. Among these forces are torsional excitations that are typically due to cogging torque and current fluctuations when a pulse width modulated (PWM) signal is used for speed control. These torsional excitations generate vibration in the motor housing that can be transmitted to other components and thus, generate noise. Electric motor structure-borne noise is an important contributor to in-vehicle noise, vibration and sound quality in various conditions such as during an idle condition.
Accordingly, there is a need to provide decoupling structure to reduce the motor structure-borne noise in engine cooling applications while constraining translation of the motor.
An object of the invention is to fulfill the need referred to above. In accordance with the principles of the present invention, this objective is achieved by providing a motor assembly having a DC motor. The motor includes a motor housing defining a stator, a rotor assembly supported for rotational movement with respect to the stator, and a shaft coupled to the rotor assembly for rotation about an axis of rotation. The assembly includes a supporting structure carrying the motor and decoupling structure. The decoupling structure mounts the motor housing to the supporting structure in a manner to provide a certain natural frequency of the motor in torsion around the axis of rotation of the shaft while providing natural frequencies higher than the certain natural frequency for degrees of freedom of the motor other than torsion. The assembly also includes pivot structure associated with the supporting structure and the motor defining a pivot between the motor and the supporting structure with a center of the pivot being aligned with the axis of rotation.
In accordance with another aspect of the invention, a method of controlling vibration of a motor assembly is provided. The motor assembly includes a DC motor having a motor housing defining a stator; a rotor assembly supported for rotational movement with respect to the stator, and a shaft coupled to the rotor assembly for rotation about an axis of rotation. The method includes coupling the motor housing to a supporting structure via springs so as to provide a certain natural frequency of the motor in torsion around the axis of rotation of the shaft while providing natural frequencies higher than the certain natural frequency for degrees of freedom of the motor other than torsion, and providing a pivot between the motor and the supporting structure with a center of the pivot being aligned with the axis of rotation.
Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification.